Improve Step 5 of onboarding with better context and hands-on guide

[keyurgolani]

Summary

• Add introduction to smolagents and InferenceClientModel to provide context before jumping into technical details
• Mark Step 5 as optional with a <Tip> callout so users know they can skip it
• Reorganize into clear sub-sections (5.1-5.6) for better readability
• Add hands-on "Try It Out!" section with a working Python script
• Improve Warning callout for port conflicts with commands for both Linux/macOS and Windows
• Provide two options when another process is using port 11434 (run on different port vs. stop conflicting process)
• Fix model.generate() call to use correct message format with type/text keys

Test plan

• Verify the Python script runs correctly with a local Ollama instance
• Confirm the MDX formatting renders correctly in the course
• Check that all links work properly